Earthworking machines, e.g., motor graders, are used quite often to cut or scrape terrain to a desired finished contour. For example, a motor grader having an earthworking blade is used to cut the contours of a road. In this application, it is desired to shape the road so that a crown exists along a longitudinal center line of the road. The crown defines a line of highest elevation along the road, thus creating downward slopes on either side of the crown. The sloped road surface can advantageously drain water off the road, thus preventing water from accumulating on the road surface.
It is common practice to position the earthworking blade on the terrain such that one end of the blade overlaps the location of the desired crown, thereby compensating for inadvertent movements of the blade as the motor grader traverses the terrain. However, this results in a tendency to lower the blade at the overlapping end to the surface of the road, thus cutting into and altering the desired crown. A skilled operator must constantly be aware of the location of the desired crown and maintain the blade so that the overlapping end is not lowered too far.
The above problem is compounded by the development of computer-aided earthworking systems. For example, in U.S. Pat. No. 5,631,658, Gudat et al. disclose a method and apparatus for operating geography-altering machinery relative to a work site to alter the geography of the site toward a desired condition. Models of the desired and actual site geographies are stored in a database. A position receiver located on the machine determines the position of the machine relative to the site. A dynamic database receives the machine position information, determines the difference between the actual and desired site models, and updates the database in real time for display or control purposes.
In automated systems such as these, as applied to the crown control application discussed above, the overlapping end of the blade is determined to be at a particular x and y coordinate. The computer-aided earthworking system then determines from its database the corresponding z coordinate as a point on the surface of the road. The system then positions the overlapping end of the blade on this z coordinate. This results in the desired crown of the road being cut into and altered.
The present invention is directed to overcoming one or more of the problems as set forth above.